I started working on the side of the spa that is next to the deck wall before we left for Estes Park and finished it when we returned. My two sons helped with this project–stretching 1/4″ hardware cloth to keep out mice and using a long metal bar to lever the spa into its final position.
I had read several blogs and articles about spa insulation. I decided to follow this advice.
Wrap foam pipe sleeves around all of the hot water plumbing pipes. The inside diameter of the pipe sleeve correlates to the outside diameter of the pipe. If you do not know which are the hot water pipes, fill up the hot tub and run the heater. The heated pipes will feel warm as they heat up. Cold water feeder pipes will always remain cold. Wrap the pipe sleeves around the hot water pipes. In most cases the sleeves come with their own taped joints that will join together once they are in place. Make sure the seam in the sleeve faces downward. Wrap the sleeves to seal them with cable ties, placed a foot apart, or use metal foil tape.
I had some high quality pipe insulation left over from the project of insulating the pipes in the crawlspace. It was made for 3/4″ pipe but it stretched around the 1″ pipes on the spa. I used the yellow plastic tape from the Restore to secure it. Then I ordered a less expensive pipe insulation that was also 1″ think but it is only R-5 instead of R-7. I ordered it a bit too large for the 2 inch pipes and had to stuff and seal the open ends with scrap pipe insulation and more tape. I insulated both the hot and cold return pipes. The cheaper insulation was also stiffer and more difficult to get around the pipes, but it is better than no insulation.
More online advice about hot tub insulation:
The tub came with foil bubble wrap under the skirting and 1/2″ styrofoam behind that. I added 3.5″ of Roxul insulation (R14) inside the styrofoam. Roxul is a mineral wool insulation. It repels water and therefore doesn’t lose its insulating value if exposed to moisture. It’s soft like fiberglass but denser and stiffer. It was easy to fit into tight spots where pipes come close to the cabinet. It can be easily cut to shape where necessary and is stiff enough that its doesn’t sag where there is no support. I installed it right up to the underside of the shell, so it also closed off the gap between the shell and the skirt. I left a gap between the shell and skirt near the blower pump so that the blower would have a supply of fresh air. I used thin wood dividers to keep the insulation away from the pump motor air intakes.
I wrapped the inside closest to the fiberglass shell with Reflectix insulation (foil bubble wrap) then replaced the styrofoam in the frame with 1 1/2″ polyiso just on the wall side and taped the seam between the panels. I left the styrofoam at the upper edge because it was glued and there is no room for the 1 1/2″ polyiso up there. I wrapped the frame on that side and the bottom with 1/4″ hardware cloth to keep critters out of the warm insulated space and stapled it to the wood siding supports. I also laid the Reflectix under the tub on top of the hardware cloth.
Then I screwed the siding on where it abuts the deck wall. When that one wall was finished, my sons took our large metal lever and lifted the tub to remove supports and shoved it against the deck wall. Nice that I had two strong men visiting to help with the project.
I have plenty of both 24 inch and 16 inch wide Roxul rock wool insulation for 6″ walls. I thought I could stuff the batts in between the hardware cloth and the Reflectix on the wall side after the siding was on, but all I got for my efforts was only a couple of feet of coverage and scraped arms from the edges of the hardware cloth.
For the other sides, I’ll put the Roxul in before the polyiso and the hardware cloth.